Integrated circuits have evolved into complex devices that can include millions of components (e.g., transistors, capacitors, and resistors) on a single chip. Photolithography may be used to form components on a chip. Generally the process of photolithography involves a few basic stages. Initially, a photoresist layer is formed on a substrate. The photoresist layer may be formed by, for example, spin-coating. A chemically amplified photoresist may include a resist resin and a photoacid generator. The photoacid generator, upon exposure to electromagnetic radiation in the subsequent exposure stage, alters the chemistry of the exposed portion of the photoresist, for example solubility or chemical reactivity, in the development process. The electromagnetic radiation may have any suitable wavelength, such as a wavelength in the extreme ultra violet region. The electromagnetic radiation may be from any suitable source, such as, for example, a 193 nm ArF laser, an electron beam, an ion beam, or other source. Excess solvent used during the coating process may be removed in a pre-exposure bake process.
FIG. 1 depicts a photoresist layer 100 on a material layer 102 formed on a substrate 104 during a prior art photolithography exposure process. Photoacid 108 is generated in an irradiated region 106 when a photoacid generator is exposed to a radiation 105. The radiation 105 has an effect of forming latent image lines 101 in the photoresist layer 100.
The photoacid 108 is primarily generated in the first region 106 of the photoresist layer 100 during light exposure processing. During the post exposure bake process, movement of the photoacid is generally random and the interface between areas within the photoresist layer 100 that include the generated photoacid 108 and areas that do not include the generated photoacid comprise an unclear boundary. For example, the random movement may result in at least a portion of the photoacid 108 diffusing into a second region 110 that may not be irradiated. The unintended diffusion may create undesired wiggling and/or an undesired roughness profile. As a result, the unintended diffusion may result in inaccurate feature transfer to the target material, which may lead to device failure and/or loss.
Therefore, there is a need for a method and apparatus to control edge straightness in latent image lines in the photoresist layer.